1. Field of the Invention
The present invention relates to printed circuit boards and more particularly, to printed circuit boards (PCBs) with coplanar waveguides and high frequency applications.
2. Related Art
Modern IC devices operate at increasingly higher frequencies. As frequencies of circuits placed on PCBs reach tens of gigahertz, the electrical characteristics of PCB traces resemble high-speed signal transmission lines, rather than DC electrical circuits. The higher frequencies and resultant shorter signal rise times expose PCB performance limitations that are manifested by signal integrity phenomena such as ringing, dielectric losses, reflections, ground bounce, and cross-talk.
Stripline, or microstrip transmission lines, are commonly used as a means of transmitting signals from one portion of the printed circuit board to another. Typically the impedance of the waveguide formed by the stripline or the microstrip structure is matched to 50 ohms.
The microstrip transmission line is a strip conductor that is separated from a ground conductor by a dielectric substrate. However, a problem with the microstrip line is that it has a high transmission loss at high frequencies.
Conventional art has attempted to deal with the problem of losses in the dielectric by turning to exotic materials with relative dielectric constant ∈r of down to approximately 2. However, these materials are typically very expensive, highly flammable, and exhibit poor peel characteristics. The capacitive effects that are created by the presence of the dielectrics, even low ∈r dielectrics, add to system losses, and degrade signal integrity.
As a result, there is a need for structures capable of transmitting high frequency signals, which minimize transmission losses, are of small size, allow for easy and inexpensive fabrication and integration, and still enable desired performance requirements to be met.